For a projection type liquid crystal display device in recent years, a high resolution light bulb device, for example, a liquid crystal panel unit is used to project image information more clearly and brightness is continuously increased to light up the projection screen brighter.
More specifically, with the widespread use of personal computers such as notebook personal computers, there is a strong demand for a small, light projection type display device with excellent portability as an image output apparatus for a notebook personal computer which is widely used for electronic presentations. Furthermore, a projection type display device, etc., for a home theater is also becoming widespread.
On the other hand, as the brightness increases, rated input power of a light source lamp also increases, which makes it more important to secure cooling performance for cooling the light source lamp, etc.
With reference now to FIGS. 5 to 7, a conventional projection typed is play device will be explained. FIG. 6 is a plan view of a conventional projection type display device using a cooling apparatus around a light source lamp used in a projection type display device that modulates light signals through a light bulb made up of a liquid crystal panel according to image information, color-combines modulated light beams of different colors after modulation, enlarges and projects the light beams on a screen through a projection lens unit. Furthermore, FIG. 7 is a right side view of the same device. FIG. 5 illustrates a conventional axial flow fan to show an overview of a cooling fan 6 which is a general axial flow fan used in the same device.
As shown in FIG. 6, the conventional projection type display device includes a light source lamp unit 1, an irradiation optical unit 2 that condenses light from the above-described light source lamp unit 1, three liquid crystal panel units 3 consisting of R, G and B liquid crystal panels as light bulbs for optically generating image information from the condensed light, a color combination system unit 4 that color-combines the optical information of the liquid crystal panel units 3, a projection optical unit 5 that enlarges and projects the image information onto a screen, a cooling fan 6 for cooling the light source lamp unit 1 and its periphery, a light-shielding member 7 for preventing unnecessary light of the light source lamp unit 1 from leaking outward and a housing 8 provided with a exhaust opening 9 for circulating exhaust air of the cooling fan 6.
Here, the cooling mechanism of such a projection type display device will be explained.
As shown in FIG. 6, the high temperature atmosphere of the light source lamp unit 1 is led through the light-shielding member 7 and exhausted out of the housing through the exhaust opening 9 provided in the housing 8 due to a pressure difference produced before and after propellers as air blowing means by rotation of the cooling fan 6. In this way, the heat of the atmosphere inside the housing 8 is transferred and cooling is realized.
More specifically, propellers 12 form an air blowing means formed integral with the rotor of a motor 11 and rotate as the motor 11 rotates. Thus, the air is circulated in the axial direction inside an air duct formed in a housing 10 that holds the motor generally aligned with the rotation center of the motor 11.
However, such a conventional projection type display device requires a large light-shielding member to prevent light from leaking toward the outside of the set through the exhaust opening that circulates exhaust air of the cooling fan, which constitutes a major limiting factor against downsizing or price-reduction of the apparatus. Further, processing speed of electronic devices such as personal computers have been drastically improved, and thus the temperature inside the housing tends to rise owing to the location of a circuit board, etc., on which the CPU and various drive ICs are mounted. For this reason, it is necessary to provide a large axial flow fan or dust-proof structure to prevent dust, etc., from entering the set, causing complexity and upsizing of the structure).
Furthermore, the above-described conventional projection type display device has excessive air blowing resistance of the cooling fan caused by such a light-shielding member, which requires high-speed drive of the cooling fan to cope with an increased amount of heat generated at the high-power light source lamp unit, producing loud noise and interfering with audiovisual functions.